[2.1 Docs] Ontology & Collaboration: RDF/SPARQL, announcement type #586

Document 2.1 ontology and collaboration additions.

Work

• RDF and SPARQL: insights endpoints and RDF 1.2 SPARQL result support (playground and MCP knowledge-graph tools already exist under how-to-guides/ontology/). Confirm OSS-vs-Collate split. PRs: OpenMetadata#28042, #33675
• Announcements type field (Information / Warning / Issue) and the ?type list filter. Page how-to-guides/data-collaboration/announcements.mdx. PR: OpenMetadata#33980

UI images needed: announcement type selector (small); RDF/SPARQL minor or none.